This invention relates, in general, to a method for polishing a semiconductor wafer and more particularly to a method for polishing a single surface of a semiconductor wafer extremely flat.
It is well known by those skilled in the art that semiconductor wafer surfaces are severely damaged by wafer thinning processes such as grinding to remove material. Semiconductor wafer polishing is a common method for removing damage from a wafer surface. Single sided wafer polishing equipment and double sided wafer polishing equipment is used by most semiconductor manufacturers. High quality single sided polishing is of particular importance to many semiconductor wafer users.
Several parameters are measured to determine the quality of a polished wafer. Total thickness variation (TTV) is the difference between the highest and lowest elevation of the polished surface of the semiconductor wafer. Taper is the lack of parallelism between the unpolished surface of the wafer and the selected focal plane. Total indicated reading (TIR) is the difference between the highest point above the focal plane and the lowest point below the focal plane (this measurement always yields a positive number). Focal plane deviation (FPD) is the greatest distance above or below the chosen focal plane (this measurement can be positive or negative). All the parameters listed above are measurements of wafer flatness. Wafer flatness is extremely important in the fabrication of high density, small geometry semiconductor devices.
Semiconductor wafers polished only on a single side are polished using a single sided wafer polishing equipment. Basically, single sided wafer polishing equipment comprises a holding chuck and a rotating element for polishing. A semiconductor wafer is placed between the holding chuck and the rotating element. The semiconductor wafer is held by the holding chuck. A polishing slurry is used in conjunction with the rotating element to remove a small amount of material from the semiconductor wafer surface leaving an undamaged surface. Single sided wafer polishing equipment is expensive and typically handles a single semiconductor wafer at a time. Single wafer handling provides a polished wafer output of typically only 10 wafers per hour. Single sided wafer polishing equipment also produces a defect on the semiconductor wafer surface commonly known as "dimpling". Finally, single sided wafer polishing equipment does not provide the required level of wafer flatness needed for the fabrication of small geometry devices.
It would be of great benefit if single sided polished wafers could be produced which reduced cost, increase throughput, and provide semiconductor wafers having less taper and increased flatness.